I just purchased some stock art on RPGNow. It is affordable, which is good. But when I finished my download all the images were under 100 dpi (they are B&W illustrations). The ads all said 300dpi, which leads me to believe I must be doing something wrong during the download process. Does anyone know what I can do differently when downloading my stock art.

What's the workflow like? You click the download button and what is the file format that you're saving? What happens next? Which program are you using to find out the resolution? What are the image dimensions (the width and height in millimeters or inches or some such), and what should they be? What are the file sizes and formats for the images?

The simplest explanation is that the images have been accidentally saved at a low resolution and large dimensions (triple the height and width they should have); if this is the case, you actually have the correct files, and you just need to resave with the right resolution to resize the images appropriately. The second likeliest case is that the files you're downloading do not actually contain 300 dpi images; this could be a mistake on the seller's end, caused by their chosen file formats and file preparation techniques. For example, if they're amateurs (I understand this is not uncommon in stock art business), they might be providing the images as pdf files that have been mistakenly distilled at a low resolution; I seem to remember that some Adobe software gives 100dpi as the default resolution for distilling, that might be the culprit if your files are in pdf format when you receive them.

The likeliest explanation on your end, on the other hand, would be if you were somehow opening preview versions of the images, perhaps directly off the Internet. "Under 100 dpi" could be what you'd get as a typical web image. So make sure that you're opening the files you downloaded and not some small preview image from the Internet.

If an analysis of the file formats and sizes, and image dimensions, verifies that your files are one ninth of their supposed size (which they'd be if the resolution is just one third of what's advertised), then the obvious course is to contact the artist/publisher and ask them what's up. They'll fix the problem for you, one would imagine.

Yeah, that's a pretty pixel-y picture. Consider: if you resize that image for 300 dots per inch, it'll still be close to 11 inches wide. The publisher's being a bit primitive in proffering the images with a screen resolution, but it's trivial for you to resize them yourself with an appropriate program.

Depending on your workflow you might now open the pdf in Photoshop and resave the images with the appropriate resolution (allowing the dimensions to retract accordingly, so the program doesn't try to create new pixels or something), or you might simply use the images as-is in your layout program, reducing their dimensions by an appropriate percentage in that. Depends on whether you trust your layout program to ignore its internal resolution correctly, and on whether it'll be too complex to do the resizing in the layout instead of a separate program.